Given the purpose of a role, can multiple characters fill that role to meet the essential requirements? Or/also, can there be multiple Protagonists if you have one Main Character? If there can be multiple Sidekicks, I don't see why there can't be multiple Protagonists or Multiple Guardians. Kinda like a team approach to fulfilling the role, or kinda like a multiple-headed creature with each head chiming in in support of the role's traits. I don't see why not. Seeing's how we're looking for essentials to be filled. Hm.

Short answer, "Yes." A group can be a character -- the "Empire" in Star Wars has all sorts of players that make up that group and work as one to stop the Rebels.

You can also have a series of character play the role of a single character function. The extreme version of this are the four ghosts in "A Christmas Carol," each one acting as the Influence Character signpost (act) by signpost (act).